1. Field of the Invention
The invention relates to an optical module, and more particularly to a focus adjustment module to adjust the intervals between optical elements.
2. Description of the Related Art
In optical apparatuses, for example a projector, a video recorder or a camera, the intervals between lenses, or a lens and an imaging sensor are used for zooming and focusing.
Referring to FIGS. 1 and 2, a conventional focus adjustment module 1 which is telescopic along an optical axle L includes a zooming motor 11, a cam 12 disposed along the optical axle L, a first lens unit 13, a second lens unit 14, a sleeve 15 disposed along the optical axle L, a focusing motor 16, a lead screw 17 disposed on the focusing motor 16, a focusing lens unit 18 and an imaging sensor 19.
The first lens unit 13 comprises a plurality of first linking pins 131 passing through the sleeve 15 and the cam 12. The second lens unit 14 comprises a plurality of second linking pins 141 passing through the sleeve 15 and the cam 12. When the zooming motor 11 drives the cam 12 to rotate, the first linking pins 131 and the second linking pins 141 link the first lens unit 13 and the second lens unit 14 to move along the optical axle L for zooming relative to the imaging sensor 19.
When focusing, the focusing motor 16 drives the lead screw 17 to adjust the interval between the focusing lens unit 18 and an imaging sensor 19 for focusing.
Thus, the cam 12 and the sleeve 15 must be linked to the first linking pins 131 and the second linking pins 141, and the lead screw 17 must be linked to the focusing lens unit 18 so that the positions of the first lens unit 13, the second lens unit 14 and the focusing lens unit 18 on the optical axial L are adjusted. As such, the conventional focus adjustment module 1 needs many elements and the volume thereof is large. Additionally, the cost for a highly precise cam 12 is very high. At present, a piezoelectric material and a liquid lens can be used to manufacture the focus adjustment module 1. However, the cost is also very high and the application field is limited.